John,  I just finished polishing the lever hardware for a 1922 Steinway
OR grand nearing completion, so the Temponamic knob is fresh on my
mind.  Typically the cylindrical shaft of the "extendable" outer knob
is designed to pull out several inches for easier operation, and push
back in for storage so that it fits under the closed keyslip.

The shaft of the outer knob section is a hollow cylinder that slides
onto the mating machined "half-cylinder" profile of the inner shaft,
and the outer shaft is locked onto the inner shaft with a small
half-cylinder "chock" that slides into the inner end of the cylinder
and is held in place with a very tiny slot-head set screw.

To remove the knob, carefully remove the tiny set screw near the inner
end of the outer knob shaft and then gently pull the knob outward, so
that the locking chock will slide out, being careful not to accidentally
drop or lose either tiny piece.  It should then be easy to clean,
polish and lubricate the workings of the knob before re-assembly.

Ralph Nielsen
http://www.historicpianos.com/